A priori and a posteriori

A priori and a posteriori ('from the earlier' and 'from the later', respectively) are Latin phrases used in philosophy to distinguish types of knowledge, justification, or argument by their reliance on empirical evidence or experience. A priori knowledge is that which is independent from experience. Examples include mathematics,[lower-roman 1] tautologies, and deduction from pure reason.[lower-roman 2] A posteriori knowledge is that which depends on empirical evidence. Examples include most fields of science and aspects of personal knowledge.

The terms originate from the analytic methods of Aristotle's organon: prior analytics covering deductive logic from definitions and first principles, and posterior analytics covering inductive logic from observational evidence.

Both terms appear in Euclid's Elements but were popularized by Immanuel Kant's Critique of Pure Reason, one of the most influential works in the history of philosophy.[1] Both terms are primarily used as modifiers to the noun "knowledge" (i.e. "a priori knowledge"). A priori can also be used to modify other nouns such as 'truth". Philosophers also may use apriority, apriorist, and aprioricity as nouns referring to the quality of being a priori.[2]


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